The present invention relates to a socket for an electrical part for detachably accommodating an electrical part such as semiconductor device (called hereunder xe2x80x9cIC packagexe2x80x9d), and more particularly, a socket for an electrical part having improved contact pins contacting terminals of the electrical part.
An IC socket as a socket for an electrical part having a conventional structure is shown, for example, in FIGS. 7 and 8, which corresponds to a structure disclosed in the Japanese Utility Model Laid-open Publication No. SHO 63-61788.
In the structure of the IC socket shown in these figures, a float plate 3 is disposed on a base 5 of a socket body 2 to be vertically movable under a state being upward urged, as viewed, and an IC package 6 is mounted on this float plate 3.
The IC package 6 includes a package body 6a having a lower surface to which a number of terminals 6b are arranged with narrow pitch between adjacent ones.
A number of contact pins 7 are electrically connected to the terminals 6b, respectively. Each of these contact pins 7 comprises a cylindrical (tubular) piece 7a, upper and lower contact pieces 7b and 7c disposed inside the tubular piece 7a and a coil spring 7d also disposed inside the tubular piece 7a so as to be interposed between the upper and lower contact pieces 7b and 7c. These contact pieces 7b and 7c and coil springs 7d are formed of conductive materials. In such structure, the upper contact piece 7b is urged upward, and the tubular piece 7a is inserted under pressure into the socket body 2, or the tubular piece 7a is idly fitted to the float plate 3 and the lower contact piece 7c is inserted into an insertion hole 9a formed to a printed circuit board 9 to thereby establish an electrical connection. The socket body 2 is fastened to the printed circuit board by means of bolts 10 or like.
Furthermore, a radiation (radiator) plate 11 is disposed above the IC package 6 so as to press the IC package 6 from the upper side thereof, and both end portions of this radiation plate 11 is depressed by a rotatable (pivotal) pressing members 12.
By depressing downward the radiation plate 11 by the pressing members 12, the IC package 6 is also depressed downward and the terminal 6b is pressed by the upper contact piece 7b of the contact pin 7. Accordingly, the IC package 6 is electrically connected to the printed circuit board 9 through the upper contact piece 7b, the coil spring 7d and the lower contact piece 7c. At this time, the upper contact piece 7b is vertically displaced and contacted under pressure to the terminal 6b of the IC package 6 by the urging force of the coil spring 7a, thus being electrically contacted thereto.
However, in the conventional example of the structure mentioned above, the contact pin 7 is composed of the tubular piece 7a, the upper contact piece 7b, the lower contact piece 7c and the coil spring 7d. Thus, the contact piece 7 has many constructional elements and assembling steps are complicated and increased.
Moreover, for the IC package 6, it is required to make small (fine) a pitch of the terminals 6a arranged to the lower surface of the package body 6a, and accordingly, it is also required to make small a pitch of the contact pins 7. Furthermore, it is required to widen or make wide an allowance (allowable range) to positional shifting of the terminal 6b, and for this reason, it is required to widen an area of a contact portion of the contact pin 7 contacting the terminal 6b of the IC package 6.
In a Ball Grid Array (BGA) type package, particularly, in order to avoid a damage to a portion near the center of the lower portion of a solder ball as terminal, it is necessary to sufficiently ensure an area of a recessed portion formed to the central portion of a contact portion of the contact pin contacting the solder ball. If be not ensured, the lower central portion of the solder ball abuts against a portion, not recessed portion, of the contact portion, and thus, this portion may be damaged.
However, in the contact pin 7 of the conventional structure, the diameter of the tubular piece 7a is larger than the upper contact piece 7b having a contact portion. Therefore, it is difficult to sufficiently secure the contact portion contacting the terminal, and hence, also difficult to make fine the pitch of the contact pin 7.
An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide a socket for an electrical part having a structure capable of reducing the number of constructional parts or elements and assembling steps thereof.
Another object of the present invention is to provide a socket for an electrical part capable of ensuring a sufficient area of a contact portion of the contact pin contacting a terminal of the electrical part with fine pitch.
These and other objects can be achieved according to the present invention by providing, in one aspect, an IC socket for an electrical part in which a contact pin electrically connecting a terminal of an electrical part and a printed circuit board is provided for a socket body of an IC socket, wherein the contact pin comprises a sleeve having a space having one end opening, a plunger inserted into the sleeve through the end opening thereof to be vertically movable and an elastic member for urging downward the plunger in an vertical attitude of the contact pin, and the sleeve is arranged to be vertically movable with respect to the socket body and is provided with a contact portion formed to an upper end thereof contacts a terminal of the electrical part to be electrically connected thereto and the plunger has a lower end contacting the printed circuit board to establish an electrical connection therebetween.
In preferred embodiments of this aspect, the plunger is arranged to be vertically movable with respect to the socket body. The sleeve and the plunger are disposed to be relatively slidable to thereby establish an electrical connection therebetween. The contact portion of the sleeve is formed with a central recessed portion and/or the contact portion of the sleeve is formed with a plurality of sharp protruded portions.
In a more detailed aspect, there is provided an IC socket for an electrical part for establishing an electrical connection between a printed circuit board and a terminal of an IC package, comprising:
a socket body to which the IC package is mounted;
a plurality of contact pins provided for the socket body through which a plurality of terminals of the electrical part are electrically connected to the printed circuit board; and
means mounted to the socket body to press the electrical part against the socket body,
each of the contact pins comprising, in a vertical attitude thereof:
a sleeve having an inner space having one end opening;
a plunger inserted into the sleeve through the end opening thereof to be vertically movable; and
an elastic member for urging downward the plunger,
the sleeve being arranged to be vertically movable with respect to the socket body and being provided with a contact portion at an upper end thereof contacting to the terminal of the electrical part to be electrically connected.
In preferred embodiments of this aspect, the means to press the electrical part is a cover member pivotally mounted to the socket body.
The sleeve is composed of a tubular member into which the plunger is fitted and the elastic member is disposed, the elastic member is a coil spring which urges the plunger downward so as to abut against the printed circuit board to establish an electrical connection therebetween.
The socket body has a base on which a plate member is rested, the plate member being formed with a through hole through which the tubular member of the sleeve is inserted.
The tubular portion is formed with an annular protruded portion to an outer periphery thereof and the plate member is formed with a stepped portion to which the annular protruded portion abuts when the tubular member is inserted into the through hole formed to the plate member to thereby restrict an upward movement of the sleeve.
The contact portion of the sleeve is formed with a central recessed portion.
According to the preferred aspects of the present invention mentioned above, since the contact pin is composed of three parts of the sleeve, the plunger and the elastic member such as coil spring, the number of constitutional elements can be reduced and, hence, assembling steps can be made simple and reduced.
Furthermore, since the contact portion is formed to the sleeve having the inner space into which the elastic member is fitted, the diameter of the contact portion can be made larger than a diameter of a contact portion formed to a plunger which is inserted into the space. As a result, an occurrence of a damage to a portion near the central portion of the terminal of the electrical part can be avoided and the allowance to the positional shifting of the terminal can be made large, thus realizing a compact structure of the terminal of the electrical part.
Furthermore, according to the preferred embodiments, the plunger of the contact pin can be pressed under pressure against the printed circuit board by the urging force of the elastic member, so that the contacting stability of the contact pin can be ensured and an invasion of a foreign material into a space between the plunger and the printed circuit board can be prevented.
Since the plunger is urged upward and the sleeve is urged downward in a state of the electrical part being accommodated in the socket body, the elastic member is compressed from its both longitudinal directions. Thus, the repulsive force is increased and, hence, the contacting stability of the contact pin can be ensured.
Still furthermore, through the relative sliding movement between the sleeve and the plunger, both the elements are rubbed to each other, realizing an electrical conductive state therebetween. This conductive path may be added to the conductive path of the sleeve, the plunger and the elastic member, whereby high frequency performance may be improved.
Still furthermore, the formation of the sharp protruded portions to the top end portion of the contact portion of the contact pin makes it possible to bite the terminal such as solder ball and, hence, effectively support the conductive state.
The nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.